7O ASA A. SCHAEFFER. 



(&) In the experiment with yellow light 397-407 the ameba 

 moved straight toward the light after the globulin was within 

 sensing range, then moved over the beam of light, after which the 

 direction of motion was changed so that the ameba moved directly 

 toward the globulin. The globulin was eaten in a typical food 

 cup. The yellow light was not deterrent in this case. But 

 another ameba reacted negatively to both yellow light and glob- 

 ulin, when presented simultaneously, but positively when 

 presented separately. The ameba was satiated or sick, for the 

 globulin was only partially surrounded. 



3. Grains of globulin and carbon were laid over beams of 

 darkness. 



(a) An ameba moved toward a dark spot on which lay a grain 

 of carbon until it came within about thirty microns of the dark 

 spot, when negative behavior set in. The ameba moved away 

 to the right 463. In the succeeding test the ameba reacted at 

 first positively to the dark spot alone, and after that decidedly 

 negatively. 



(&) A piece of globulin was laid on the dark spot, to the right 

 of the ameba. The ameba moved directly toward the dark spot 



globulin though it seemed to have been slightly deterred by 

 the dark area, for the ameba broke up into two pseudopods 495 



and just when the dark beam was reached a little later, a 

 small side pseudopod appeared. The globulin was however 

 finally ingested. In another experiment the globulin was 

 placed near the far edge of the dark spot 522. The behavior 

 of the ameba became very irregular as it moved near the dark 

 beam. Soon a pseudopod was sent out straight toward the 

 globulin, but it was presently retracted and the ameba moved 

 off to the left, veering to the right. There can be no doubt of the 

 strongly deterrent effect of the dark beams. There can also be 

 no doubt of the strongly attractive effect of the globulin. 



SUMMARY. 



i. Ameba senses beams of light of twenty microns' diameter 

 that pass no nearer to the ameba than 100 microns or 150 microns. 

 In nearly all cases under these conditions the ameba moves 

 directly toward the beam. When the ameba comes into contact 



